Add a small ground plane. Aluminum foil on a suitable support, piece of
plywood etc., would work fine.

Deacon Dave

joe bob wrote:

i have a 5/8 vhf antenna (with coil at bottom) with nmo mount. if i cut the
wip down to 1/2 wave will it work without a ground plane? i want to put it
on my fiberglass boat.

i see marine antennas that are 1/2 wave with a coil at the bottom. i would
like to adapt a antenna i allready have.